The first two Bristol Type 171 helicopters were powered by a single 450 h.p. Wasp Junior radial engine. One, G-ALOU, seen here, was originally given the RAF serial number VL963 and made its first flight in February 1948. All subsequent Type 171s were powered by the 550 h.p. Alvis Leonides engine. G-ALOU was the first British helicopter to receive a certificate of airworthiness.